Π-conjugated materials have attracted considerable attention because they offer the potential for lower cost and more flexible approaches for the fabrication of components or devices, such as, for example, organic thin film transistors/organic field-effect transistors (OTFT/OFET), organic photovoltaic solar cells (OPV) or organic light emitting diodes (OLED).
The drive to use these materials stems from the fact that π-conjugated materials are much less expensive to generate compared to highly crystalline inorganic semi-conductors. The π-conjugated materials can also be used to make devices with relatively inexpensive fabrication methods. In particular, most organic materials used in device fabrication are soluble in one or more common organic solvent and this allows for the possibility of solution processing which can produce many devices at a fraction of the cost. Additionally, most devices require an annealing step to reach high performance that is generally at high temperatures (at least 500° C. for silicon), but the temperature required is much lower for organic semi-conductor materials. The lower annealing temperatures of organic materials allows for flexibility in the choice of substrate for organic devices, and thereby enables the use of materials such as transparent plastics that could not withstand the high annealing temperature of silicon.
One disadvantage with current techniques for the fabrication of organic semi-conductor and photovoltaic devices is that organic solvents commonly used in the fabrication process have associated health and safety issues in the work place and environmental issues relating to safe storage and disposal.
Furthermore, although the processing temperatures required are lower than for inorganic semi-conductor materials, often temperatures approaching or in excess of 100° C. are still utilised during the fabrication processes for organic semi-conductor and photovoltaic devices.
There is therefore a need for improved techniques for the fabrication of organic semi-conductive and photovoltaic devices that are effective, safe (i.e. they obviate the need to use harmful organic solvents) and that enable lower processing temperatures to be used.